When utilizing scrap aluminium, there exists the problem of separating from the aluminium during the melting process the contaminations consisting of foreign metals having a greater specific gravity than aluminium and of other impurities for the purpose of obtaining for further processing an aluminium of maximum possible purity.
For melting such scrap aluminium, there were used up till now hearth furnaces having a melting chamber, the bottom of which is inclined and is heated by burners. The melting chamber is charged with the scrap aluminium which must be covered by a layer of melting salt for preventing oxidation of the aluminium during the melting process effected by means of the burners. On account of the aluminium having a lower melting temperature than its contaminations, the molten aluminium flows downward along the inclined bottom into a storage basin, whereas the contaminations, being still in a solid condition, remain resting on the bottom and must manually be removed from the melting chamber via lateral doors after having finished a heat. The use of such a known melting furnace for melting scrap aluminium suffers from various drawbacks. For example, manual removal of the residues from the melting chamber is a laborsome and time-consuming operation. The periods of disuse of the furnace are thus long.
Furthermore, the burner flames heat in a furnace of this known type only the surface of the scrap aluminium contained within the melting chamber, so that the heat supplied is only poorly utilized and the major portion of this heat is exhausted by the hot effluent gas. Such a hearth furnace thus has a poor efficiency.
There are further known rotary furnaces, in which the drum is rotated around its longitudinal axis and is supported for being swivelled or tilted, respectively, around a swivel axis transversely arranged relative to the longitudinal axis. In a known rotary furnace of this type, charging and discharging of the drum is effected via one and the same opening provided at one front side and having there arranged a swing-out burner, whereas at the opposite front side there is only provided a discharge opening for the effluent gases.
There are also known rotary furnaces which are provided with one opening at each of both front sides, noting that the opening provided on one front side is used for charging the furnace and for accommodating the burner and the opening provided at the other front side is used for discharging the furnace and for removing the effluent gases. There is also known a tiltable rotary furnace, in which the charging opening, via which the effluent gases are withdrawn and which can be closed by a lid, is provided on one front side of the drum and the discharge opening is provided at the other front side of the drum.
All these known rotary furnaces are of only limited utility for melting scrap aluminium contaminated by foreign metals or other accompanying matter because, in particular, the iron contained in the scrap aluminium becomes quite easily alloyed during heating with the aluminium material and thus the purity of the molten aluminium material is adversely affected.